Mobile data in Germany? (but D1/D2 only)

[inquisitor]

Originally Posted by fuxoft

a) Can I buy callYa 5/15 SIM card in any Vodafone shop, without being a German citizen, and use it immediately?

Yes, but it would be cheaper to buy a Fonic SIM, since with Vodafone you would need to buy a 7-day-session for € 9.95, while Fonic will charge only € 2.50/day, so for your stay it would only cost € 7.50.
Further with Fonic you can call home to the Czech Republic and to the rest of the EU for just € 0.09/min (landlines) or € 0.29/min (mobiles). Details on Fonic are available at Germany - Fonic - Prepaid Wireless Internet Access
Please be aware, that with Fonic you will need to call customer care and ask them to switch your data tariff to "Tagesflat".

b) Does the default callYa price include some amount of credit or not? Can I top up directly in the store, while buying the card?

At least those prepaid SIMs offered online come with € 10 of credit. Of course you can add credit in any Vodafone shop or buy vouchers nearly everywhere. For details see Germany - Vodafone Web Sessions - Prepaid Wireless Internet Access

c) Are all INCOMING calls to this SIM free while I use it in Germany?

Incoming calls are always free with European operators, as long as you stay in the country your SIM is from.